1. Field of the Invention
Typically, an intake system provided on an automobile engine is equipped with silencing means in an intake air passage so as to decrease suction noises caused due to pulsations of intake air introduced in the intake air passage. When a suction means is provided in the intake passage, the suction means is provided with a certain length and volume, forming a structure with closed ends which is connected to the air intake passage. The intake system with such a volume forming structure is installed in an engine room of a vehicle together with the engine. To install the engine, together with the intake system and its associated elements, in the small space of the engine room, the intake system, with a silencing means, must be compact in structure and small in size.
2. Description of Related Art
In order for the intake system to be made small in size, the intake system may include a particular type of air cleaner provided with a space which functions to lower the level of intake suction noises. Such an air cleaner may be referred to as a "built-in silencer" type. The built-in silencer type of air cleaner helps make the intake system small in overall size. Such an intake system is known from, for instance, Japanese Unexamined Utility Model Publication No. 60-102,456.
Noises caused in an intake passage include noises produced by pulsations of air in the intake passage, mechanical noises caused by vibrations of mechanical members, such as a pipe forming the intake passage or an air cleaner case, and noises due to an air flow and the air cleaner case. Some noises, such as the noises due to the mechanical vibrations of the air cleaner case and the intake passage pipe, can be silenced effectively by silencing means specifically disposed at a proper location outside the air cleaner; for instance, such silencing means may be disposed at an air inlet of the intake passage through which air into the air cleaner is introduced. For this reason, it is preferable for the intake system to include the silencing means in a portion in which the air inlet of the intake passage is formed. However, since the engine room generally has no room left available around the air inlet, it is difficult to install the silencing means, which must be in communication with the air inlet of the intake passage, without enlarging the engine room and/or rearranging various elements associated with and surrounding the air inlet.
If the engine room is enlarged so as to accommodate the silencing means, which must be in communication with the air inlet of the intake passage, the part formed by the air inlet becomes low in mechanical strength or rigidity.